1. Field of the Invention
The instant invention relates to a stack battery structure. In particular, the invention relates to a battery structure that possesses a high energy density and avoids the existence of a die volume by stacking battery cell electrodes.
2. Related Art
For an ordinary rechargeable battery, the positive/negative electrode 10a, 10b coating and assembly methods are first done by mixing positive/negative-pole active substances, polymeric binder, and a conducting agent into a positive/negative-pole active material 12a, 12b to be coated onto a current collector 11a, 11b using a coating machine. The coating pattern is shown in FIG. 1 or FIG. 2.
FIG. 1 shows a coating of a single material at intervals, while FIG. 2 shows a continuous coating of a single material. The coated positive/negative electrode 10a, 10b is further put under pressure and striped. Polymeric separator membranes are employed to separate them. Afterwards, the structure is rolled into a circle or an ellipse for making a cylindrical or prismatic battery.
Since recent developments in electronics are toward thinner, lighter, and smaller equipment, the design of a rechargeable secondary battery then has stricter requirements on the weight, energy density, and space of the battery. The early secondary battery structure has a circular shape, as shown in FIG. 3. The positive electrode/polymeric separator membrane/negative electrode module is rolled into a spiral 20 and put into a cylindrical metal case 21. Technically, this spiral structure is relatively mature. But it obviously can not prevent the existence of a die volume 22 and results in spatial waste.
Therefore, batteries with rectangular cases are then invented, as shown in FIG. 4. Currently, prismatic batteries are widely used in the design of lithium ion batteries and nickel hydrogen batteries. There is less spatial waste using a rectangular case for battery cell stacking. Yet, if the positive/negative electrode is rolled into an elliptical spiral and then put into a rectangular metal case 21a, there is still some die volume 22a within the battery.
In view of the foregoing, recent battery assembly is performed by stacking and pressuring, which is similar to the stacking in polymeric batteries, as shown in FIG. 5. In principle, the battery formed by stacking electrodes 30 can reach the closest stacking; namely, the space is more effectively used. With the encapsulation of an aluminum foil case 31, the total weight of the battery can be lowered. So this could increase the energy density of the battery. Nonetheless, the electrodes and polymeric separator membranes (PE, PP, or non-woven cloth) are not adhesive to each other in current battery designs, so current rechargeable batteries (nickel hydrogen battery, lithium ion battery) can not be fabricated by stacking and pressuring. The polymeric battery can be manufactured by stacking and pressuring because the polymeric electrolytic membranes (similar to separator membranes) bear a stronger adhesivity. Yet since the electrodes need to be stacked and pressured with the polymeric electrolytic material (membranes), the polymeric binder on the positive/negative electrode need to be increased, which unfortunately lowers the ratio of active material on the electrodes. Thus, the polymeric battery has a lower energy density than the lithium ion battery does. Moreover, the increase of polymeric binder on the electrodes lowers the electrical conductivity on the electrodes, resulting in difficult charge/discharge processes in large polymeric batteries.
Therefore, how to perform the closest packing on the positive/negative electrodes and the polymeric separator membranes without increasing the amount of polymeric binder on the electrodes becomes the most urgent issue nowadays.
It is an object of the present invention to provide a stack battery structure that can avoid a die volume due to spiraling of conventional battery cell electrodes and also increase the energy density of the battery.
The present invention uses stacking to prevent the formation of the die volume when electrodes are spiraled into a circular or elliptical shape.
Furthermore, to increase the energy density of the battery, the stack battery disclosed in the present invention is characterized in that (a) the binder is separated from the active material; (b) by rearranging the positions of the binder, the positive/negative electrode can be glued with the polymeric separator membranes via the binder in the process of stacking and pressuring; and (c) the percentage of the active material in each unit of weight is not affected and the binding action due to stacking and pressuring has nothing to do with the active material.
In a preferred embodiment of the invention, the binder layer is formed on a single surface of the current collector on the battery electrode by die coating or screen printing.
In another preferred embodiment of the invention, the binder layer is formed on both surfaces of the current collector on the battery electrode by die coating or screen printing.
In yet another preferred embodiment of the invention, the binder layer is formed on the peripheral of the electrode material, on the two symmetric side edges, or distributed along the diagonals on the surface of the electrode so that the positive/negative electrode can be tightly bound to the polymeric separator membranes.
The stack battery structure disclosed in the invention achieves the following effects:
1. A binder layer is formed on the current collector surfaces of the battery electrodes for binding with the positive/negative electrode and the polymeric separator membrane. Therefore, the binding of stacking and pressuring has nothing to do with the active material and accordingly there are much more choices for the materials of the binder layer and the polymeric separator membrane.
2. The present invention can be applied to lithium ion batteries, lithium polymeric batteries, nickel hydrogen batteries, and capacitors.
3. The energy density of the battery can be increased by stacking battery electrodes.
4. The problem of the die volume caused by spiraling electrodes can be avoided.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.